Yes you can.
If you have set up dual boot, you will come up with a window as shown when you start up.
If you want to go to Windows 7 you click on Windows 7 or, on Windows 8 otherwise. If you do not take any action within a certain time it will boot to Windows 8.
Even if you are in Windows 8, you can access the files and folders in Windows 7. If you are the administrator you can access files and folders.
How do I set up dual booting?
These two posts show you, how you can.
This post shows how you can set up your Windows 7 computer for dual booting.
The following post shows how you can install Windows 8 after preparing the computer as shown previously. I used a evaluation copy but you can use the full version you have.